Limit switch



Jan. 24, 1967 G. HEWETT 3,300,597

LIMIT SWITCH Filed Nov. 25, 1964 2 SheetsSheet 1 /N VE/V TOQ W/LL/J 6. HEM/77 ATTORNEY Jan. 24, 1967 w. e. HEWETT LIMIT SWITCH Filed Nov. 23, 1964 3,300,597 LIMIT SWITCH Willis G.. Hewett, 233 Ave. G, Fort Dodge, Iowa 50501 Filed Nov. 23, 1964, Ser. No. 412,973 3 Claims. (Cl. 200-47) This invention relates to improvements in electric switches and more particularly to switches that can be operated by a moving object from any direction. This improved switch has been especially designed for, and will be described in relation to use in, the production line of gypsum boards, but it will be understood and appreciated from the description which follows that it is not necessarily limited thereto.

In the manufacture of gypsum boards for example, the finished boards which are generally of four by eight foot dimensions and from one-half to three-eighths inch thick are moved on a combination of rollers and belts over a production line which includes various stations for folding one board onto another, rejection of defective or damaged boards and packaging. In passing through these several stations, the boards will at times make a ninety degree change of direction in their path of travel and for this purpose certain machinery as presently used provides a system of reversible rollers for selectively moving the boards in two respective opposite directions and a system of belt conveyors disposed for movement transversely of the direction afforded by the rollers. Such rollers are provided with electrically actuated means for vertical height adjustment and when carrying boards, these rollers are on a higher plane than the belts. By actuation of the adjusting means, the rollers are lowered below the plane of the belts so that boards initially moving on the rollers are lowered onto the belts for movement in a transverse direction.

To actuate the adjusting means for the roller apparatus referred to, it is customary to employ a limit switch at designated points relative to the several stations on the production line and such switches as presently used embody the use of an upstanding spring-loaded lever or push rod, usually of nylon or the like, Which is known as a wobble stick. These switches are so located that the wobble stick extends upwardly from the production line in the path of travel of the boards and are bent, deflected or moved away from their normal vertical position by contact from the moving boards whereby such bending effects the actuation of the switch. Such wobble sticks are designed to freely snap back into place when cleared by the board.

In the use of the wobble stick type of limit switch, as indicated, it has been observed that they wear very rapidly and are exceedingly susceptible to breaking and to bending beyond the capacity of the springs to return them to off position so that their useful life is of a relatively short duration. This has resulted in the necessity for replacing them as often as weekly with not only a resulting high replacement expense but additional expense due to loss of production time while the factory operation is shut down for switch replacements.

With the above observations in mind, one of the important objects contemplated by this invention is the provision of an improved limit switch that is durable in constr-uction, efiicient in operation and designed to function adequately under the severest conditions of rough treatment over long periods of time with trouble free operation.

Another object inherent in this invention is the provision of a limit switch as characterized that includes a spring-load push type plunger rod provided with an improved contact head which is so designed that it effective- Patented Jan. 24, .1967

ly causes operation of the push rod when contacted at any point through 360.

Further objects of this invention are to provide a limit switch of the above class which is simple in design, economical in construction, easy to install since it does not have to be oriented in any particular direction and extremely eflicient for its intended purpose.

To attain these objects and such further objects as may appear herein, or be hereinafter pointed out, reference is made to the accompanying drawings forming a part hereof, in which:

FIG. 1 is a fragmentary plan view of a combination roller and belt production line machine shown only for the purpose of illustrating one environment in which the present invention can be used,

FIG. 2 is a perspective view showing a preferred embodiment of my new limit switch,

FIG. 3 is an enlarged cross sectional view taken on the line 33 of FIG. 2 and showing the switch in neutral or off position,

FIG. 4 is a view similar to FIG. 3 but showing the plunger rod depressed so that the switch is actuated, and,

FIG. 5 is a reduced fragmentary perspective view showing a modified contact cap on this switch.

Referring to the drawings, the plan view of the machine 10 which is shown in FIG. 1 illustrates an important area of use for my new limit switch 12 and while no invention is claimed in machine 10, a brief description of its function will serve to facilitate the understanding of switch 12.

Machine 10 so far as shown includes a plurality of spaced parallel conveyor belts 14 each movable over a suitable platform support (not shown) from left to right as viewed in FIG. 1. The longitudinal area covered by the belts 14 is divided into different processing areas or stations designated by the numerals 16, 18 and 20. Area 16 will be referred to as the intake or receiving station, 18 as the folding station and 20 as the reject station. A further packaging station is included beyond station 20 but it is not shown as the three stations which are illustrated are sufficient for purposes of this disclosure.

Intermediate the belts 14 in stations 16 and 20 there are a pair of spaced rollers 22, parallel to the belts 14 and mounted at respective opposite ends to bar supports 24 for rotation about their [longitudinal axes and are chain driven 26 by suitable drive means (not shown). Electronically actuated means (not shown) are provided for vertically moving the several rollers 22 so they may be moved either above or below the plane of belts 14 at times and means are also provided to selectively rotate rollers 22 in either direction. It will thus be appreciated that when a pair of boards 28 and 30, for example, are to be moved, they will travel in one direction on the rollers if such rollers are elevated above belts 14 and will travel in a transverse direction thereto on the belts when the rollers are below the belts. Boards being processed are usually moved in pairs as shown and station 18 provides folding arms 32 and 34 which operate to fold one board onto another in a manner which is not material to this invention.

Boards 28 and 30 as shown in FIG. 1 are finished products which enter station 16 from prior processing onto rollers 22 and then must move on belts 14 through stations 18 and 20 and on to further stations not shown. If any board is defective or damaged, it is withdrawn at station 20 and because such boards are processed in pairs, a replacement board may be sent back into the production line at station 20. It will thus be appreciated that the elevating and lowering mechanism must be actuated from time to time as the necessity for raising and lowering rollers 22 arises and for this purpose limit switches are dis- '3 posed at selected points relative to such rollers so as to intersect the path of movement of the boards, and which are electrically connected to the mechanism to be actuated. It is in this respect that my new limit switch has special utility to overcome the dis-advantages of limit switches presently in use as heretofore indicated.

With references now more particularly to FIGS. 2-4, switch 12 includes a rectangular closed casing 36 having a removable side plate 38 and provided on opposite sides with apertured ears 48 and 42 to facilitate mounting to any suitable support. Preferably, switch 12 is mounted in the position shown in FIG. 1 and thus for purposes of description the top of casing 36 will be identified with the numeral 44 and the bottom by the numeral 46. A suitable opening 47 is provided in the bottom 46 of casing 36 for the reception of an electric cable (not shown) in a well known manner. A tubular housing 48 is mounted within casing 36 so as to project upwardly through top 44 as at 50 and downwardly through bottom 46 as at 52 and is provided with a sidewall opening 54 as best seen in FIGS. 3 and 4. A plunger rod 56 is reciprocally mounted in housing 48 through end 50 and its normal or neutral position as shown in FIG. 3 is maintained by the spring means 58 located in the bottom portion of housing 48. Such housing is externally threaded at its bottom end 68 to receive the cap 62 and tension adjusting means 64 for spring 58 is provided in a well known manner. The lower end of the plunger rod 56 is notched 66 and is designed to register with opening 54 in housing 48 when the switch 12 is in neutral or off position.

Plunger rod 56 is provided with a longitudinal slot 68 which moves relative to a stop member in the form of a screw 70 that is mounted to housing 48 so as to extend through slot 68 and is secured to the casing 36. The bottom end of slot 68 is located so that the force of spring 58 cannot move rod 56 past its neutral position as described. Without such stop means 70, spring 58 would tend to push rod 56 completely out of housing 48.

The extreme upper end of the plunger rod 56 carries the novel contact cap 72 which is of a pyramid design having the substantially four triangular faces 74 converging upwardly to the top point 76. By this arrangement, it can be appreciated that contact against any one of the faces 74 will result in movement of rod 58 into housing 48 against the spring 58.

Also mounted within casing 36 is a microswitch member 78 of a type which is commercially available and to which no invention is claimed per se. Switch 78 includes the box or housing 88 for the switch mechanism (not shown) and is attached to case 36 by a pair of screws 82. Contact points 84 externally of housing 80 are for lead wires from any apparatus to be actuated in a well known manner. Switch 78 is normally open and is olosab'le by movement of the spring loaded arm 86 that carries a roller member 88 on its outer end. The roller 88 end of arm 86 is normally'urged slightly away from housing 80 when switch 78 is open and a movement of only one-sixteenth of :an inch of arm 86 towards housing 86 is sufficient to close the switch 78 and correspondingly close any circuit in which it may be imposed.

Switch 78 is so llOCEltBd that roller 88 registers with opening 54 in tube 26 and thus is in rollable contact with the plunger rod 56. In the neutral position of rod 56 as described, roller 88 will rest in the notch 66 of such rod which affords adequate movement of arm 86 away from housing 80 to open switch 78. As rod 56 is depressed, roller 88 is cammed out of notch 66 so that it rolls against the full diameter portion of such rod which provides sufiicien-t movement of arm 86 towards housing 80 to CilOSfi switch 78. The rolling contact between roller 88 and rod 56 eliminates any unnecessary wear and breakage on switch 78 due to any over-travel of the rod which may be necessary to accommodate switch 12 to a proper position relative to the height of rollers 22 with which it functions. Upon release of contact against cap 62, rod 56 is returned by spring 58 to its neutral position which is determined by stop 70 as described above.

It has been determined from actual use, that once spring 58 is properly adjusted, no further adjustments are generally required and spring 58 need only be strong enough to lift the weight of rod 56 and cap 62. By this arrangement, very little pressure is required to depress rod 56.

With reference to FIG. 5, I have shown a modified contact cap 90 which is dome-like in design so as to present a radially inclined surface downwardly in all directions from its apex point 92 and thus be capable of depressing rod 56 irrespective of its direction of contact by any moving objects such as boards 28 and 30.

It will of course be understood that switch 12 is imposed in any circuitry used for the purpose of actuating the mechanism required for raising and lowering the rollers 22 and that the purpose of switch 12 is merely a means to open and close any such circuitry upon contact by the moving boards 28 and 38 whereby such boards can move from station 16 to station 18 automatically or from station 20 to a next station (not shown) automatically. In regard to the withdrawal of any defective board at station 20 as previously pointed out, it should be mentioned that while switches 12 in station 20 operate as described above, a further manually operated normally open switch (not shown) is generally disposed in series with switch 12 so that the operation of switch 12 at station 20 will be ineffective against rollers 22 at such station unless an inspector determines that a particular board should be withdrawn and closes the manual switch. Thus, in station 20, switches 12 must be susceptible of operation from at least two different directions and in this regard, the advantages of switch 12 are quite apparent.

It will be noted that all working parts of switch 12 are enclosed in casing 36 by which the switch is mounted and kept substantially dust free and thus from the foregoing description, it is thought a full understanding of the construction and operation of this invention will be had and the advantages of the same will be appreciated.

It will be understood that the phraseology employed herein is for the purpose of description and not for limitation and that modifications and changes in the construction and arrangement of this invention can be made within the scope of what is claimed, without departing from the spirit and purpose thereof. It is thus intended to cover by the claims, any modified forms of structure or mechanical equivalents which may be reasonably included within their scope.

I claim:

1. In a limit switch, the combination of:

a casing,

a normally open electric switch in said casing designed for connection in an electric circuit,

said electrical switch having a spring load actuating arm movable to a closed position and carrying a roller on one end, I

an elongated enclosed housing in said casing having and open end terminating exteriorly of said casing,

said housing having a sidewall aperture disposed within said casing,

a spring loaded plunger reciprocally mounted within said housing so that one end of said plunger in its neutral position projects beyond the open end of said housing,

the other end of said plunger being provided with a notch adapted to register with said aperture in neutral position,

said roller, being disposed within said aperture and said notch when said plunger is in neutral position whereby said electric switch is open,

a contact cap on the projected end of said plunger, said cap being of a pyramid design so that contact therewith from a direction transverse to the longitudinal axis of said plunger from any point in a 360 circle will effect depression of said plunger into said housing, and

movement of said plunger into said housing causes said roller to be cammed out of said notch to rollably engage the widest diameter of said plunger whereby said arm is moved sufficiently to close said electric switch.

2. A device as defined in claim 1 including means automatically stopping said plunger at its neutral position when any contact force against said cap is released.

3. In a limit switch, the combination of:

a casing,

a normally open electric switch in said casing designed for connection in an electric circuit,

said electrical switch having a spring load actuating arm movable to a closed position,

an elongated enclosed housing in said casing having an open end terminating exteriorly of said casing,

said housing having a sidewall aperture disposed within said casing,

a spring loaded plunger reciprocally mounted within said housing so that one end of said plunger in its neutral position projects beyond the open end of said housing,

the other end of said plunger being provided with a notch adapted to register with said aperture in neutral position,

a cont-act cap on the projected end of said plunger, said cap having radially inclined sides extending downwardly and outwardly from an apex point so that contact against said cap from any transverse direction will etfect movement of said plunger into said housing,

References Cited by the Examiner UNITED STATES PATENTS 2,181,829 11/1939 Jefiirey. 2,209,805 7/1940 Beck 200-47 X 2,984,720 5/1961 Fisher 200-153 X 3,145,275 8/1964 Gildart 2006l FOREIGN PATENTS 598,690 5/1960 Canada.

OTHER REFERENCES Product Engineering, issue of November 12, 1962, pages 84-101.

References Cited by the Applicant UNITED STATES PATENTS 2,648,234 8/1953 Lester. 2,675,435 4/ 1954 Framhein. 2,822,436 4/ 1958 Towle.

BERNARD A. GILHEANY, Primary Examiner. T. MACBLAIN, H. A. LEWITTER, Assistant Examiners.- 

3. IN A LIMIT SWITCH, THE COMBINATION OF: A CASING, A NORMALLY OPEN ELECTRIC SWITCH IN SAID CASING DESIGNED FOR CONNECTION IN AN ELECTRIC CIRCUIT, SAID ELECTRICAL SWITCH HAVING A SPRING LOAD ACTUATING ARM MOVABLE TO A CLOSED POSITION, AN ELONGATED ENCLOSED HOUSING IN SAID CASING HAVING AN OPEN END TERMINATING EXTERIORLY OF SAID CASING, SAID HOUSING HAVING A SIDEWALL APERTURE DISPOSED WITHIN SAID CASING, A SPRING LOADED PLUNGER RECIPROCALLY MOUNTED WITHIN SAID HOUSING SO THAT ONE OF SAID PLUNGER IN ITS NEUTRAL POSITION PROJECTS BEYOND THE OPEN END OF SAID HOUSING, THE OTHER END OF SAID PLUNGER BEING PROVIDED WITH A NOTCH ADAPTED TO REGISTER WITH SAID APERTURE IN NEUTRAL POSITION, A CONTACT CAP ON THE PROJECTED END OF SAID PLUNGER, SAID CAP HAVING RADIALLY INCLINED SIDES EXTENDING DOWNWARDLY AND OUTWARDLY FROM AN APEX POINT SO THAT CONTACT AGAINST SAID CAP FROM ANY TRANSVERSE DIRECTION WILL EFFECT MOVEMENT OF SAID PLUNGER INTO SAID HOUSING, ONE END OF SAID ARM BEING DISPOSED WITHIN SAID APERTURE AND SAID NOTCH WHEN SAID PLUNGER IS IN NEUTRAL POSITION WHEREBY SAID ELECTRIC SWITCH IS OPEN, MOVEMENT OF SAID PLUNGER INTO SAID HOUSING BY A CONTACT FORCE AGAINST SAID CONTACT CAP CAUSES SAID ARM TO BE CAMMED OUT OF SAID NOTCH TO ENGAGE THE WIDEST DIAMETER OF SAID PLUNGER WHEREBY SAID ARM IS MOVED SUFFICIENTLY TO CLOSE SAID ELECTRIC SWITCH, AND MEANS AUTOMATICALLY POSITIONING SAID PLUNGER AT ITS NEUTRAL POSITION WHEN ANY CONTACT FORCE AGAINST SAID PLUNGER IS RELEASED. 